Analysis and redesign of air level detector

Abstract: Gambro is one of the biggest developers and manufactures of machines for hemodialysis treatments in the world. One component on their machines, the air level detector (ALD), has been identified to have a possibility to be further improved from usability perspective. The ALD is located at the front of the machine and has the function to hold the venous drip chamber in place and detect whether or not it contains fluid. The venous drip chamber is a part of the blood line, which is a disposable product that is changed between every treatment. The function of the drip chamber is to capture air that is left in the blood line, so it does not reach the patient. The ALD should be compatible with a universal blood line, which means that the size and stiffness of the drip chamber may vary. The ALD detects the content of the drip chamber with ultrasonic sensors. When air gets captured by the drip chamber the blood level decreases, and if it gets too low the ALD alarms and stops the treatment. The most important improvement areas that Gambro has identified with the ALD are that it may make use of less force to apply the drip chamber and to further simplify cleaning of it. They have also identified a possible improvement to avoid the hatch breaking. The purpose of this project is to analyze why improvements may be needed and find a new solution. The analysis started with a finite element simulation of the ALD to find out its weaknesses. Then interviews were performed with service staff and clinical advisors to see what they thought should be improved with the ALD. The last step of the analysis was to perform simple tests of the ALDs from Gambro and also from other manufacturers. The conclusions from the tests pointed at that there is a lot of potential for improvements. A lot of concepts were generated in the development process and two were chosen to be further developed. The development method of these was to make a new design, do a simple simulation, study the stresses, and then redesign the concept. Of the two concepts that were further developed, one had significantly lower stresses than the other and was therefore chosen to be the final design. This chosen concept was then tested, both practically and virtually. The practical test was performed together with a sensor, to see that they work together. The virtual tests were performed with finite element simulations of different scenarios that could appear during the use of the ALD. The conclusions of the tests were that the ALD works together with the sensor, and has stresses below the fatigue limit.